Spinning of polypropylene



United States Patent 3,233,023 SPINNING 0F POLYPROPYLENE I Richard William Harold Benson, Harrogate, England, as-

signor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain No Drawing. Filed Feb. 21, 1963, Ser. No. 260,330 Claims priority, application Great Britain, Feb. 27, 1962,

6 Claims. (Cl. 264-168) is now widely known as isotactic polypropylene.

Fibres or filaments spun from isotactic propylene polymers may be utilised in several ways. They may be drawn and used as continuous filament yarns or they may be drawn .and cut into short lengths and further processed as staple fibre in which form they may be processed on conventional textile machinery either alone or mixed with other natural or synthetic fibres. Staple fibres may be utilised for producing filling materials of high bulk. It is an essential part of the staple fibre process that a wavy form should be imparted to the fibres to assist their processing on conventional textile machinery, especially when mixed with natural fibres having this wavy or crimped form. The crimping of the fibres also imparts softness and bulk to yarns produced from them, leading to greater warmth in fabrics produced from such yarns. The process of crimping the fibres has hitherto been an additional step included after the drawing stage in staple fibre production. Filaments spun from i-sotactic polypropylene may be utilised also as textured or bulked filament yarns which are produced by, for example, a false-twisting process after the drawing stage of the filament yarn prowss.

I have found by conducting the spinning process in such a way that the spun yarn has a birefringence between 10 10- and 19 10- and an intrinsic viscosity between 1.0 and 3.0 and then cold-drawing the spun yarn to draw ratios of 1.2 to 4.0, that on relaxation of the yarn it will spontaneously take up a helical form. I have also found that it is preferable to stabilise the helical form by a heat treatment for example by treating the relaxed yarn in air at 140 C. for about twenty minutes.

According to the present invention I provide a process for the production of fibres or filaments of isotactic polypropylene as hereinbefore defined having a helically crimped form characterised in that the crimped form is spontaneously developed by spinning the filaments of isotactic polypropylene at such a temperature and at such a throughput from polymer of an intrinsic viscosity such that the intrinsic viscosity of the spun yarn is in the range 1.0 to 3.0 preferably 1.5 to 2.5 and the birefringence of the spun yarn is between 10 10- and 25 19- and then drawing the spun yarn to 1.2 to 4.0 times its original length the stretched yarn thereafter being allowed to relax freely and quickly.

Birefringence, which indicates the degree of orientation of the spun filaments, may be measured by means of a 3,233,023 Patented Feb. 1, 1966 polarising microscope fitted with a suitable compensator. The intrinsic viscosity, which is conveniently measured in solution in decalin at 135 C., has the meaning defined in the standard reference textbooks, for example on page 309 of the 1953 edition of Principles of Polymer Chemistry by P. J. Flory.

While very satisfactory spontaneous crimping of the polypropylene yarn is obtained by the process hereinbefore described I have found that under certain conditions the spontaneous crimping effect may be brought about without the second stage drawing. In a specific embodiment of this form of my invention I have spun isotactic polypropylene, having an intrinsic viscosity of 3.4, at a temperature of 252 C. and a wind up speed of 2,000 feet per minute, The spun yarn produced had a birefr-ingence of 17 10 and an intrinsic viscosity of 2.25. Upon release of the winding tension the spun yarn developed a helical crimp which, on stabilisation for about 20 minutes at a temperature between 100 C. and 140 C., increased to a level corresponding to 13% crimp as hereinafter defined.

I have found also that some control of the environment of the threadline in the region of maximum drawing by controlled cooling or heating allows a further control of the birefringence of the spun yarn and also of the spontaneous crimping effect obtained on relaxation. It is clear that there exists a value'of draw ratio, dependant upon the values chosen for the intrinsic viscosity and birefringence of the spun yarn, which will lead to optimum de velopment of spontaneous crimping. By proper control of these factors it is possible to vary the degree of spontaneous crimping from almost none to very high crimp densities.

In a specific embodiment of my invention I spin isotactic polypropylene having an intrinsic viscosity between about 1.5 and 2.5 at a temperature between 200 and 300 C. and a wind-up speed between 1,000 and 5,000 feet per minute so that the spun filaments have a birefringence between 15 X10- and 20X 19- and an I.V. between 1.2 and 2.5. These filaments are then cold drawn using a draw ratio between 1.2 and 4.0 and upon relaxation f the drawn yarn spontaneous crimping of the filaments took place. Degrees of crimping between about 5 and 50 turns/inch have been attained by this technique.

The degree of crimping may be expressed either as the number of turns per inch or as the percentage crimp which is expressed by the relation where L is the length of the filament with the crimps present 1. is the length of the same filament when extended just sufficiently to remove the crimps.

When a second stage drawing step is used I have found that the temperature of the heated pin, roller or other device whereon drawing takes places, may be varied over a wide range of temperature from about 10 C. to about 140 C. and a spontaneous crimping effect is still obtained on release of the drawing tension. I prefer to use a drawing temperature between about C. and C.

Improved spinning and processing as .hereinbefore described may be usefully integrated with the melting/compressing procedure for polypropylene which is the subject of British specification 818,100. A suitable apparatus comprises a screw extruder, from which molten poly propylene is supplied to a spinneret via a metering pump. Filtration of molten polymer is desirable both before and after it passes through the metering pump, the temperature of the first filter can, if desired, be well below that of stage drawing was omitted, the winding tension of the spun yarn'was released and the yarn allowed to relax freely at 140 C. to develop the full helical crimping effect.

the second filter. With such an apparatus polypropylene The following table shows the percentage crimp deof high intrinsic viscosity, for example, 3.0 to 4.0, may veloped in yarns spun under various conditions. be used as starting material and thermally degraded in the melter to give the desired level of intrinsic viscosity in the spun yarn.

To .obtain a spun yarn having the hereinbefore speci- 1O fied birefringence and intrinsic viscosity the conditions of spinning are varied to suit the particular isotactic poly- Spinning Windmp y g f propylene used and the degree of spontaneous crimping Temperature pee A I Percenta e required. I have found, for example, that starting with 2232 figg Crimp polypropylene of intrinsic viscosity between 1.0 and 6.0, X suitable spinning conditions are a spinneret temperature between 175 C. and 320 C., preferably 180-290 C. 5 250 2 M5 19 5 and a wind-up speed between about 1,000 and 4,000 feet 3:: 5:888 i3; i2 3 per minute, 8 268 3,000 1. 95 16 Crimped fibres or filaments produced according to the g process of my invention are very suitable for use in textile applications, especially for preparing carpets, blankets, apparel fabrics or other textile products where the crimped structure leads to such desirable properties as What I claim is: resilience, cohesiveness or bulk of the staple or continuous 25 1. A process for the production of crimped filaments filament yarns comprising such crimped fibres, either of isotactic polypropylene comprising producing isotacalone or mixed with natural fibres or other synthetic fibres. tic polypropylene filaments having an intrinsic viscosity Because of their enhanced bulk and resilience fibers proof between about 1.5 and 2.5 and a birefringence of beduced by the process of present invention are particularly tween about 10 10 to l9 10- said producing step suitable for use as filling material in, for example, pilincluding the steps of melt spinning a polypropylene of lows and cushions. intrinsic viscosity between 1.0 and 6.0 at a spinneret tem- The examples which follow illustrate but in no way perature between 175 C. and 320 C, to form filaments limit our invention. and winding up the filaments at between about 1000 and 5000 feet per minute, said process further comprising sub- Ej'amples 1'4 sequently drawing the filaments at between 10 C. and Isotactic polypropylene having an intrinsic viscosity 140 C. at a draw ratio of between about 1.2 and 4.0 and (in Decalin at 135 C.) of 3.2 to which 0.4% of a suitrelaxing the drawn filaments to produce spontaneous able antioxidant and 0.1% of a suitable peptiser (a subcrimping. stance added to promote thermal degradation of poly- 2. A process according to claim 1 wherein the spinpropylene'from a higher to a lower molecular Weight) 40 neret temperature is 240 C. to 260 C.-, the spun filahas been added was fed into a screw melter from which ments have an intrinsic viscosity of 1.8 to 2.2, the windthe molten polymer was supplied to a metering pump and up speed is 1000 to 3500 feet per minute, the birefrinthence through a filter consisting of 1020 mesh sand to gence of the filaments is 15X 10 to 19x10 and the a two hole spinneret (hole diameter 0.015 inch). The draw ratio is 1.25 to 2.0, screw melter, metering pump and filter were enclosed in 3. A process according to claim 2 wherein the intrinsic an electrically heated jacket which was maintained at the viscosity of the polypropylene being spun is about 3.2 required spinning temperature. The spun yarns were and wherein the drawing is carried out at about C. at then cold drawn using a water bath at 90 C. at the rea draw speed of about 200 feet per minute. quired draw ratio and at a draw speed of 200 feet per 4. A process according to claim 1 wherein the reminute. The drawn yarns were then relaxed quickly by 50 laxed yarn is stabilized by heating to a temperature of cutting the yarn off the draw bobbin and stabilised by C. to 140 C. heating in air at 140 C. for twenty minutes. 5. A process for the production of crimped filaments The table which follows shows the effect of spinning of isotactic polypropylene comprising producing isotactic temperature and wind-up speed on the intrinsic viscosity polypylene filaments having an intrinsic viscosity of beand birefringence of the spun yarn and the effect of draw 55 tween about 1.5 and 2.5'and a birefringence of between ratio on the degree of spontaneous crimping obtained, about 15x10" and 10 10 said producing step in- Spun Yarn Properties Spinning Wind-11p Temperature Speed (feet Draw Percentage Turns 0.) minute) Intrinsic Birc- Ratio Crimp per Inch Denier Viscosity fringence Examples 5-8 Isotactic polypropylene having an intrinsic viscosity of 3.4 (in Decalin at C.) was spun with the same equipment as in the preceding examples. The second cluding the steps of melt spinning isotactic polypropylene at 250 C. to 270 C, and winding up the filaments at 1120 to 3000 feet per minute, said process further comprising relaxing the yarn directly after the wind-up step.

5 6 6. A process according to claim 5 wherein the relaxed 827,409 2/1960 Great Britain. yarn is stabilized by heating to a temperature of 100 C. 875,103 8/1961 Great Britain. to 140 C.

References Cited by the Examiner ALEXANDER H. BRODMERKEL, Primary Examiner.

UNITED STATES PATENTS 5 MORRIS LIEBMAN, Examiner.

c. B. HAMBURG, K. W. VERNON, A. LEAVITT,

Assistant Examiners.

3,093,444 6/1963 Martin 18-54 XR FOREIGN PATENTS 1,297,364 5/1962 France. 

1. A PROCESS FOR THE PRODUCTION OF CRIMPED FILAMENTS OF ISOTACTIC POLYPROPYLENE COMPRISING PRODUCING ISOTACTIC POLYPROPYLENE FILAMENTS HAVING AN INTRINSIC VISCOSITY OF BETWEEN ABOUT 1.5 AND 2.5 AND A BIREFRINGENCE OF BETWEEN ABOUT 10X10-3 TO 19X10-3, SAID PRODUCING STEP INCLUDING THE STEPS OF MELT SPINNING A POLYPROPYLENE OF INTRINSIC VISCOSITY BETWEEN 1.0 AND 6.0 AT A SPINNERET TEMPERATURE BETWEEN 175*C. AND 320*C. TO FORM FILAMENTS AND WINDING UP THE FILAMENTS AT BETWEEN ABOUT 1000 AND 5000 FEET PER MINUTE, SAID PROCESS FURTHER COMPRISING SUBSEQUENTLY DRAWING THE FILAMENTS AT BETWEEN 10*C. AND 140*C. AT A DRAW RATIO OF BETWEEN ABOUT 1.2 AND 4.0 AND RELAXING THE DRAWN FILAMENTS TO PRODUCE SPONTANEOUS CRIMPING. 